Modeling it as two spheres, one 16 km across the other 12 km, with a density the same as water, its total mass would be about 3*10^15 kg. At a distance of 8 km

Modeling it as two spheres, one 16 km across the other 12 km, with a density the same as water, its total mass would be about 3*10^15 kg. At a distance of 8 km from the center of mass, the escape velocity [0] would be about 7 meters/second or 16 miles/hour. But the asymmetry of Ultima Thule means that its gravitational field would be weird. Not like a sphere at all. So the acceleration of gravity and escape velocity would vary a lot from place to place. [0] https://en.wikipedia.org/wiki/Escape_velocity https://en.wikipedia.org/wiki/Escape_velocity